The invention relates generally to communication systems and more particularly to communications systems that employ echo detection and echo cancellation.
Packet switched networks for transmission of voice signals and other information have gained tremendous impetus in recent years, wherein, for example, coded audio packets, such as coded speech packets or other audio packets are routed through public (internet, voice over IP) or private networks (intranets) out to a destination point. With conventional systems, it is assumed that speech quality improvement such as acoustic echo cancellation, noise suppression and volume level adjustment has been addressed prior to encoding speech packets at the point of packet origination by an originating unit such as a wireless or non-wireless Internet appliance, portable communication device, non-portable device, or any other suitable device.
As known in the art, speech samples are echo canceled (due to the presence of acoustic echo from, for example, a sending unit (far end) as received by a receiving unit (near end) noise suppressed and level adjusted (automatic gain control) followed by encoding to produce encoded audio packets for transmission to a destination unit. Near end encoded audio packets are typically those transmitted to a network element from, for example, a wireless mobile unit whereas far end encoded audio packets are those encoded by another wireless mobile unit that is communicating with the transmitting mobile unit. In an internet protocol system, transmitted speech packets are routed to a receiving unit through a network element. For example, an ISP gateway routes the packets through the Internet or intranet to an ISP gateway associated with a receiving unit where the speech packets are subsequently transmitted to an end user for decoding. Hence, speech samples are echo cancelled, noise suppressed and encoded to produce encoded audio packets for transmission to another user. Although it is assumed by the infrastructure, such as the ISP gateway, that echo cancellation has been adequately addressed at the point of origination by the transmitting unit, a problem can arise if an inadequate level of echo cancellation is performed by the sending unit. Accordingly, it would be desirable to provide an independent echo cancellation process, preferably by an immediate infrastructure unit (for example, an immediate ISP gateway) associated with the transmitting unit.
To provide echo cancellation, it has been proposed to insert background noise packets in place of packets that contain undesirable amount of echo. However, such systems, typically require the decoding of an encoded speech packet prior to performing echo detection and cancellation and then re-encoding the speech packet for routing to a destination unit. The re-encoding process can consume enormous computational resources and tandem vocoding, such as decoding and encoding then decoding, can undermine overall speech quality.
Accordingly, gateways or other network elements that employ packet decoders that decode incoming encoded speech packets and perform echo cancellation and noise suppression and then re-encode the echo cancelled packets for those packets determined to require echo cancellation can add additional delays due to the re-encoding of the modified speech packets.
Also, it is typically more desirable to insert background noise as part of an echo cancellation process than utilize pure erasure packets since erasure packets can yield a complete muting of speech, which may be objectionable from a subjective listening point of view. Therefore, some level of background noise, sometimes referred to as comfort noise packets, may be more desirable than utilizing erasure packets.
Accordingly, it would be desirable to eliminate the need for re-encoding of audio packets and still facilitate a suitable form of echo cancellation without adding significant delay or unsuitable processing demands.